The present invention relates to direct current (D.C.) motors. More particularly, the present invention relates to a multi-phase bipolar brushless D.C. motor having a stator constituted by an armature, a rotor constituted by embedded permanent magnets, and a plurality of windings connected in parallel resulting in increased efficiency and ease of manufacturing.
In a conventional shunt motor, field coils (exciting coils) are wound on the rotor in order to have the proper number of poles. Coils attaching the brushes to the rotor are wound on the rotor so that as the rotor is rotated energy or power is produced. However, these motors present certain drawbacks. For example, alien substances such as dust can become lodged between commutator segments or the brush. These components must be replaced due to the contact with the dust and the breakdown of insulation or the wear thereof within the motor.
U.S. Pat. No. 4,882,524 discloses a multi-phase bipolar brushless D.C. motor using stator windings sub-wound in series, an encoder wheel having angled slot edges, and a photosensor moved within the slot for adjusting timing to overcome drawbacks of existing D.C. motors. The ""524 patent called for the use of whole phase reduction for commutation timing such that xe2x80x9cMxe2x80x9d phases would be activated xe2x80x9cMxe2x88x921/Mxe2x80x9d percent of the time. However, this motor had problems associated with current spikes and poor conductance during commutation, resulting in poor power production. The motor also was difficult to manufacture.
Accordingly, what is needed is an improved brushless D.C. motor of improved performance which is easier and less expensive to manufacture than prior motors. The present invention fulfills these needs and provides other related advantages.
The present invention resides in a multi-phase bipolar brushless D.C. motor in which the embedded permanent magnet is used for the rotor, the winding is wound on the stator as the independent winding and subwound in parallel, the commutation encoder is fixed on the shaft of the rotor to be rotated and has a rectangular cut out of the annular ring which can be varied to control commutation interval, and the photo-sensor is coupled operatively thereto to be connected with the driving circuit. Such a motor is smoothly started and rotated with high torque at low speed and high power at high speed with a simple construction and low cost of manufacture.
More particularly, the stator is constituted by M phases, each phase having a plurality of windings which are connected in parallel and being connected independently of the winding connection of the other phases. The rotor is rotatably coupled to the stator and has xe2x80x9cNxe2x80x9d embedded permanent magnet poles. A commutation encoder is fixed at one end of the rotor shaft outside the motor and is generally cylindrical in form. The commutation encoder comprises a circular plate and an annular ring, the annular ring having light shielding portions and light detecting portions, each light detecting portion has opposite vertical edges. The light shielding and light detecting portions function, respectively, as the non-sensing and sensing area. A photo-sensor is coupled operatively with the commutation encoder and is constituted so that two photo-transistors are provided with respect to each phase. Each photo-transistor is arranged in M phases, in turn, one by one at intervals of predetermined shaft angle so as to produce a positive pulse when registered with the sensing area of the commutation encoder. An electronic commutator is constituted in such a manner that four power transistors are connected across the winding coil of each phase of the stator. Two of the transistors of each phase are connected to one photo-transistor of the photo-sensor so that each phase is provided with two photo-transistors so as to perform the determination of the current direction according to the positive pulse of the photo-transistors, thereby flowing the alternating current through the winding coil to drive the motor. Finally, an electric power source is connected in parallel to each phase of said electronic commutator.
If in this motor the stator winding is arranged as the lap winding, the motor produces the sinusoidal torque ripples thereby to be adapted for the micro-motor. If instead the stator winding is arranged as the wave winding, the motor produces the trapezoidal torque ripples to be adapted for the power motor.
The present invention is devised to be made into a bipolar system so that the copper loss of the exciting coil can be minimized, thereby increasing the efficiency, and to make into polyphase so that the utility of the coil can be increased, thereby making the compact design of the motor possible and improving the torque ripple. Also in this motor the commutation system comprises a commutation encoder, a photo-sensor and a electronic commutator which are simply and safely constituted so that the starting and rotation characteristics of the motor can be improved. The motor is smoothly started and rotated, with high torque at low speed and high power at high speed. The simple construction of the motor also reduces the cost of production.
Other features and advantages of the present invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.